Graduate Program
Chemistry
Degree Name
Master of Science (MS)
Semester of Degree Completion
2012
Thesis Director
Edward Treadwell
Thesis Committee Member
Kraig Wheeler
Thesis Committee Member
Sean Peebles
Thesis Committee Member
Mary Konkle
Abstract
Phosphorus ylides have been utilized in three synthetic approaches; two involving the synthesis of photochromic cinnamaldehyde semicarbazones and a final scheme towards the synthesis of the isomalabaricane natural products. The targeted cinnamaldehyde semicarbazones varied both in the length of the conjugated system as well as the position and type of phenyl ring substituents, because these variations could impact their degree of photochromicity. The three step synthesis of the extended cinnamaldehyde semicarbazones involved a Wittig condensation, hydrolysis of acetal protecting group, and formation of imine and was completed in respectable cumulative yields; 42.4% yield for semicarbazones with n = 1 double bonds, 61.9% yield for a semicarbazone with n = 2, and 33.5% yield for a semicarbazone with n = 3. A faster, more economical purification method involving filtrations for removing Ph3P=O was employed, compared to the alternative SiO2 gel column chromatography.
After at least 1-1.5 weeks, "light" and "dark" forms of the semicarbazones were examined and the photochromicity quantified. In total 24 semicarbazones were made and of those 20 exhibited photochromicity to some degree. Our data contradicted the work of Heilbron et al., in that 4-methoxycinnamaldehyde semicarbazone was more photochromic than 2-methoxycinnamaldehyde semicarbazone. Visual comparisons, the Behr color system, UV-Vis absorption data in CH3CN, and Spartan calculations were used to investigate the photochromic color change between the "light" and "dark" versions of semicarbazones from n = 1 to n = 3. It was found that extending the conjugated system, and adding OMe groups to the phenyl ring, all produced quantifiable shifts in photochromicity between the "light" and "dark" versions of the semicarbazones,yet the position of OMe groups on the ring was more important than the number. We were unable to observe the "switch" from dark to light form by either UV -Vis or 13C NMR, and while Spartan calculations were useful in showing the most likely conformational changes, the calculated ~Amax's didn't match the experimental ~Amax's.
A crystal structure of 2,4,6-trimethoxycinnamaldehyde semicarbazone (JMS 18-9) showed planarity from the ring to the imine group, only straying from planarity by a slight 6° bend between the carbonyl and the primary amine of the semicarbazone subunit, that is hydrogen bound to a second 2,4,6-trimethocycinnamaldehyde semicarbazone unit.
A second synthesis for extended cinnamaldehyde semicarbazones required the preparation of a 4C phosphorus ylide instead of a 2C ylide starting material. Following literature precedence cis-1,4-butanediol was monosilylated, converted to an allylic chloride, and then to a 4-(diethylphosphono)-2-butenol in a 39% overall yield. Chlorination instead of the bromination as done by Sun et al. was more cost effective, yet was more troublesome in obtaining pure halide. The use of impure alcohol didn't allow for oxidation to the butenal.
The third project involved studies toward the synthesis of stellettins. This involved the synthesis of 1,3-bisphosphonoacetone (BPA), in 70.7% overall yield from 1,3- dichloroacetone using Corbel's route. Monocondensations of BP A attempted using Masamune-Roush conditions did not yield products, but model studies using triethyl phosphonoacetate gave evidence of product formation with 2-chloro-cyclohexanone, cyclohexanone, 2-nitrobenzaldehyde, p-nitroacetophenone, 2-methylbutyraldehyde, and crotonaldehyde. Optimized experimental conditions included using DMSO instead of CH3CN, and premixing and heating to reflux LiCl, the phosphonoacetone, DBU and DMSO for 15-45 minutes before adding the various ketones/aldehydes. Unfortunately when the BP A was employed under the optimized Masamune-Roush conditions no reaction occurred and only the starting material, elimination product, or dicondensate were recovered. The same is true when other condensations conditions, including Buehl, Wittig, and strong base, were attempted.
Recommended Citation
Saathoff, John M., "Utilization of phosphorus ylides towards the synthesis of extended cinnamaldehydes and stellettins" (2012). Masters Theses. 934.
https://thekeep.eiu.edu/theses/934
